Precision measurement of ℏ/<i>m</i><sub>Cs</sub> based on photon recoil using laser-cooled atoms and atomic interferometry
The recoil of an atom due to the absorption of up to 64 photons is measured, using laser-cooled cesium atoms which are made to interfere in an atomic fountain. Measurement of the photon recoil allows a determination of ℏ/ m Cs , and hence the fine-structure constant. The measurement is described and a detailed theoretical and experimental study of potential systematic errors is presented. A relative precision in the photon recoil measurement of 0.1 ppm is obtained in two hours of data collection. The measurement is currently 0.85 ppm below the accepted value of ℏ/ m Cs . We cannot now formally ascribe a systematic error, but suspect that the bulk of the discrepancy is due to imperfections of the interferometer beams used to induce the Raman transitions.